Carboxylated latex products include dipped products such as balloons, gloves, fingerstalls and condoms; extruded products such as rubber threads and rubber pipes; cast- molded products such as balloons and toys; and whole rubber products and products having rubber surfaces such as rubber sheets, hoses and draw cloths. Carboxylated latex products are apt to have adhesive surfaces which can negatively affect the manufacturing of the products or produce defective articles. Further, they are not ideal for producing products having a desired shape such as non-adhesive rolled fingerstalls.
Heretofore, to overcome these defects, adhesion preventing agents have been used. Adhesion preventing agents have generally been powdered substances called dusting powder (or simply powder). The powder is generally mica, talc, calcium carbonate, white carbon or corn starch. The powder, however, can spread to articles in contact with the latex product and become the cause of various problems if the article is a precision instrument. Also, the appearance of the latex product is damaged. In July 1999, the FDA issued a regulation on medical rubber gloves stating that the powder quantity on synthetic rubber medical gloves should be 120 mg or less per glove. For natural rubber medical gloves, the regulation stated that the soluble protein be 1200 μg per glove or less to prevent the latex allergy resulting from the proteins. A shift from natural rubber gloves to synthetic rubber gloves is anticipated. Thus, making synthetic rubber products non-adhesive is an important technical issue to be solved.
The general method of adhesion prevention, other than the use of powder, includes halogenation by post-chlorination treatment. For example, U.S. Pat. Nos. 3,411,982 and 3,740,262 disclose that halogenation makes the surface of rubber gloves slippery. U.S. Pat. No. 4,304,008 discloses halogenation, in place of powder, facilitates donning rubber products. U.S. Pat. No. 3,740,262 discloses halogenating gloves where the outside surface is powder-free and the inside surface is powdered.
Halogenation is a method in which a thin layer of halogenated rubber is formed on the product surface to prevent adhesion and blooming. This method is fairly widely used, providing a rubber product having a clean surface free of powder. However, when the degree of halogenation is too high, discoloration can occur, the surface can become brittle and cause cracks, or heat resistance can deteriorate. Further, there is the danger that any contacting metal may be corroded. Above all things, many users hesitate to use such products because of their negative environmental impact.
U.S. Pat. No. 4,304,008 discloses surgical gloves wherein the inside layer comprises a natural rubber and the outside layer a halogen-resistant silicone. The inside layer is halogenated to give a non-adhesive property.
The deficiencies of halogenation are set forth in U.S. Pat. No. 5,284,607. In the patent, medical gloves are formed using an acid-soluble powder, which is then dissolved by treating with an acid such as nitric acid. Thereafter, the gloves are chlorinated by a bleaching agent.
There are a variety of improvements in the methods for manufacturing rubber products, which use powders or substances having particulate structures.
U.S. Pat. No. 4,070,713 discloses medical gloves comprising two layers, i.e., outside and inside layers, of elastic substances. In the inside layer, a particulate substance such as zinc oxide or titanium oxide is firmly embedded and partially exposed to come in contact with the skin.
U.S. Pat. No. 4,143,109 discloses a manufacturing method related to the above-mentioned patent.
U.S. Pat. No. 5,138,719 discloses a method for making powder-free gloves, fingerstalls and the like from latex and microcapsules. The microcapsules are disersed and distributed in the latex so that their concentration may increase from the outside surface of the product toward the inside surface thereof, to build a concentration gradient. The microcapsule concentration is high on the inside surface, and this gives a good lubricious property and ease in donning without the use of powder.
U.S. Pat. No. 5,881,386 discloses gloves having two layers, with the two layers comprising polyvinyl chloride and polyesterpolyurethane. The inside polyesterpolyurethane layer is incorporated with a particulate substance of 1 to 75 μm.
Japanese Patent Application Laid-Open (Kokai) No.11-12823 discloses a technology for manufacturing working gloves with improved dusting properties by dipping the inside surface in a treating agent containing a powder of 0.1 to 1.5 μm followed by drying. The working gloves, used for clean rooms, are manufactured from polyvinylidene chloride paste sol.
Japanese Patent Application Laid-Open (Kokai) No.11-61527 discloses rubber gloves excellent for donning and doffing, which have a slippery resin layer, having been dipped in an aqueous dispersing liquid containing a synthetic rubber latex that is not coagulated by a coagulant contained in the gloves themselves, and containing an organic filler.
Japanese Patent Application Laid-Open (Kohyo) No.9-501983 discloses a water-dispersible silicone modified dispersion powder composition and a method of manufacturing it, and describes that the composition can be used as an antiblocking agent.
In recent years, products have been developed with various substances coated on the surface of latex products.
U.S. Pat. No. 4,310,928 provides surgery gloves by dispersing an oil and fat or lipophilic substance in a coagulation liquid and coating it on the surface of natural rubber. To prevent separation of the oil and fat or lipophilic substance, a surface active agent is added to the coagulation liquid.
U.S. Pat. Nos. 5,780,112 and 5,974,589 disclose a method of attaching a high density straight-chain hydrocarbon polymer, in particular polyethylene, to the surface of a natural rubber by chlorine generated by acidifying a hypochlorite. The latex product thus treated is non-adhesive without the use of powder.
Japanese Patent Application Laid-Open (Kohyo) No.11-507085 discloses a flexible copolymer coating which can be bonded firmly to the surface of a rubber article and extend, without separation, from the bonded surface. The patent, taking into consideration the need to remove the latex product from the dipping former and dry and wet wearing conditions, discloses an emulsion type copolymer between a reactive, low surface energy monomer, preferably a silicone oligomer, and an alkyl acrylate and a reactive hard monomer.
There are many disclosures on the methods for preparing powder-free gloves by coating a hydrophilic hydrogel forming polymer on the rubber surface and curing the polymer layer. Examples include U.S. Pat. Nos. 3,326,742; 3,585,103; 3,607,473; 3,745,042; 3,901,755; 3,925,138; 3,930,076; 3,940,533; 3,966,530; 4,024,317; 4,110,495; and 4,125,477.
Further, U.S. Pat. No. 4,499,154 discloses a method of manufacturing a talc-free product by immersing a dipping former in a natural rubber latex, leaching the product in hot water, impregnating the product with a dilute acid, neutralizing the surface with water or an aqueous alkali solution, dipping in a hydrophilic hydrogel formable polymer such as a copolymer of 2-hydroxyethylmethacrylate and methacrylic acid or 2-ethylhexylacrylate and a crosslinking agent thereof, heating the polymer layer to fix it to the rubber, vulcanizing the rubber, removing the product from the dipping former, coating it with a silicone containing a surfactant, and providing heat. This method also discloses that the lubricious property for wet hands is improved by crosslinking the layer of the hydrogel polymer of the invention and, thereafter, treating it with a cationic surfactant such as a long chain aliphatic amine. The patent also discloses that impregnating the rubber surface with an aluminum salt after acid treatment is preferable. This method can produce powder-free rubber products, but it includes many steps and raises the manufacturing costs excessively. Moreover, it cannot be used for products, which should not include silicone.
U.S. Pat. No. 4,575,476 discloses that the coat layer of a specific 2-oxyethyl methacrylate hydrogel polymer that has a good lubricious property for use with dry hands. Further, by treating the above-mentioned hydrogel layer with a surfactant, in particular with a cationic surfactant and a long chain aliphatic amine, the lubricious property for use with wet hands is improved.
Furthermore, by treating the product with a silicone containing surfactant, the adhesiveness of the surface, without the hydrogel layer, is markedly improved.
U.S. Pat. No. 5,688,855 discloses that the hydrophilicity of a solid surface gives lubrication to the surface in the presence of water and that a hydrophilic concentration gradient is automatically generated within a coating by dissolving in one solvent a hydrogel forming polymer component and a water-soluble polymer component that has a low compatibility with the former component, coating them on the surface of a rubber product, and evaporating the solvent to cause phase separation of the two components.
Japanese Patent Application Laid-Open (Kokai) No.11-269708 discloses gloves laminated with a lubricant layer of a rubber or resin containing collagen on the inside surface of gloves provided with a base layer of a rubber or polymer.
One problem with coating the rubber surface is that layer separation can occur when the rubber is extended.
U.S. Pat. No. 4,499,154 discloses reinforcing the adhesion of a coating by undercoating an acid on the rubber surface.
W093/06996-A1 proposes using, as a coating, a polymer having a repeated structure of specific ether groups and ester groups.
U.S. Pat. No. 4,548,844 discloses improved adhesion between a rubber layer and a hydrogel layer through acid treatment. It also discloses that, by undercoating an aluminum cation or a cation of trivalence or more, prior to the coating of the hydrogel polymer or by adding it to the hydrogel polymer, the adhesion of the rubber layer and the hydrogel polymer is enhanced. It is presumed that this is caused by a hydroxy or carboxyl group in the hydrogel polymer being bonded to a protein in the rubber latex.
Japanese Patent Application Laid-Open (Kokai) No.6-70942 discloses a multilayer product comprising a first layer formed from a natural rubber, a second layer of a natural rubber, polyurethane, poly(acrylamide/acrylic acid) and polyethylene oxide, and a third layer of an acryl copolymer and fluorocarbon telomer resin. The product can be donned under dry or wet conditions without the use of powder.
Japanese Patent Application Laid-Open (Kokai) No.10-95867 discloses production of powder-free medical gloves by coating a lubricating composition comprising a first and second composition on the surface of an elastomeric product on the wearer's side, the inside. The first composition comprises at least one compound selected from the group consisting of acetylene diol, organosilicone, amino modified silicone, and cationic surfactant. The second composition is at least one compound selected from the group consisting of cationic surface active agent, organosilicone, amino-modified silicone and acetylene diol.
Japanese Patent Publication (Kokoku) No.7-4405 discloses a method of treating a surface with a modified polysiloxane.
The methods for manufacturing rubber products containing no dusting powder include a method in which a bivalent coagulant metal salt, such as calcium nitrate, and a latex stabilized by adding a water soluble surfactant stable against the metal salt, preferably a nonionic surfactant or a resin polymer, are brought into co-existence in a coagulation liquid. A dipping former, coated with the coagulant, is dipped in the latex to coat one side of the rubber product. Although this method fails to make the rubber product substantially non-adhesive, it is possible to make the rubber product non-adhesive by adding a peeling or anti-adhesion agent to the coagulant composition as a third component.
U.S. Pat. Nos. 3,286,011 and 3,411,982 to Kavalir et al. disclose the above-mentioned technology. The patents, however, fail to make the product powder-free because it uses powder as the peeling agent.
The patents disclose that polyvalent metal salts like calcium, magnesium and aluminum can be used as the latex coagulants.
The above-mentioned U.S. Pat. No. 4,310,928 discloses a method of fabricating surgery gloves, which can be removed from a dipping former by dispersing a lipophilic substance into the coagulant liquid, such as calcium nitrate.
Japanese Patent Application Laid-Open (Kohyo) No. 10-508899 discloses a method for producing a rubber article free of powder by adding to the coagulant an acrylic emulsion copolymer coating composition and a silicone emulsion. The coating composition is made by copolymerization of a reactive silicone acrylate, an alkyl acrylate and a hard monomer, but such a composition is a known substance. The patent clarifies that the release becomes easy only when the silicone emulsion is added to the composition and that the gloves performs well under dry-type conditions.
EP 640,623 discloses a coagulant for natural rubber comprising a salt-stable polychloroprene or polyurethane and a bivalent metal salt. Powder-free rubber gloves can be manufactured by further adding to the coagulant a peeling agent consisting of a polyethylene wax emulsion and a cationic surfactant.
In Japanese Patent Application Laid-Open (Kokai) No.11-236466, surfactants and various waxes such as polypropylene wax emulsion, instead of a polyethylene wax emulsion, were employed as an adhesion eliminating agent or releasing agent. The cationic surfactant functions to stabilize the polychloroprene added to the coagulant and functions as a releasing agent between the polychloroprene and the dipping former, having a greater affinity for the dipping former than the pertinent polymer.
Japanese Patent Publication (Kokoku) No.2-42082 discloses a coagulant composition formed by adding a latex and a surfactant or bivalent or trivalent metal salt into water.
In Japanese Patent Application Laid-Open (Kohyo) No.9-511708, the Teague method is used in the manufacture of polyurethane coated gloves. Namely, a first layer is formed by dipping a former in an aqueous dispersion liquid or emulsion of a polyurethane polymer or copolymer. The first layer is dipped in a coagulant then a latex compound to form a second layer. This application also discloses a method of forming a lubricating polymer layer over the second layer.
There is disclosed technology for making two powder-free gloves which use novel raw materials.
U.S. Pat. No. 5,851,683 proposes a special successive copolymerization polymer to make powder-free gloves comprising a thermoplastic elastomer for use in clean rooms.
Methods of preventing the adhesion of emulsion/latex products are important to both manufacturing and use of the products. Although various proposals have been advanced, many of these technologies are considerably complicated. A method that is simple, effective and economical has not been developed. One reason for this is that the main material is a natural rubber latex with a strong adhesive property with complicated causes for creating adhesion. Due to this, the treatment materials and techniques for preventing adhesion can be complex.
The present invention, taking into consideration the above-mentioned current status of adhesion treating technology, provides novel powder-free, non-adhesive carboxylated latex products and novel methods of manufacturing the same. Further, the present invention provides latex products having excellent durability without sulfur vulcanization.